The invention disclosed and claimed herein pertains to a system for optical heterodyne imaging. More particularly, the invention pertains to an optical heterodyne imaging system for viewing an object through a medium or environment containing diffused dynamic particles.
The range at which an optical system viewing through a diffusive medium may form an image of an object is substantially limited by the phenomenon of forward scatter, and, if the object is illuminated by light projected from the viewing system, by the phenomenon of backscatter. A diffusive medium is a medium such as fog or seawater, which contains diffused particulate matter, and a dynamic diffusive medium is a medium in which particles are in constant random motion. Forward scatter is the scattering of light transmitted from an object to the viewing system as the result of random refractions by the particles, and some of the scattered light is sensed by the viewing system. While some of the light transmitted from the object will reach the viewing system without interacting with any particles, and will therefore provide an image of the object, the sensed scattered light will degrade the image. If the viewing system is more than a limited distance from the object, the image will be totally unviewable. For example, if seawater contains an amount of silt or other refractive particulate matter, a conventional viewing device such as a television camera would be unable to distinguish an object located more than 15 attenuation lengths away.
Backscatter is the scattering of light projected from a source of light by the particles of a diffusive medium, where some of the light is reflected back toward the source. It is clear that backscatter will further degrade an image of an object which is viewed by a system which must illuminate the object.
Some techniques are presently available for overcoming the detrimental effects of backscatter in a diffusive medium such as seawater. For example, volume scanning or range gating may be employed. However, as far as is known, no system or techniques are presently available for overcoming the degradation of an image viewed through a diffusive medium which is caused by the phenomenon of forward scatter.